Heat sink



FIG. 1 is a perspective view of a heat sink of the present design;

FIG. 2 is a top view of the heat sink of FIG. 1, the opposite bottom view being a mirror image thereof; and,

FIG. 3 is a front view of the heat sink of FIG. 1, the rear, left and right side views of the heat sink of FIG. 1 being identical thereto.

Any parts shown in broken lines form no part of the claimed design. 

The ornamental design for a heat sink, as shown and described. 